calculation of end-end interaction energy nanotubes

[Zexter]

Hi

I just need to calculate the tip tip interaction between two cappped cnt.I have a capped structure of the cnt. So if I need to calculate the interaction between the nanotube is it enough to select the total energy alone in my calculation. I need only the interaction potential between the two

I have only one capped cnt. how to make a mirror image of the same cnt so that their caps face each other. Any help in the procedure to do so would be helpful. Since translating the cnt in builder is not helpful as when the file is saved and reopened the untranslated structure peeks out.

[Zexter]

Hi

 If i wanted to calculate interaction energy between the two capped nanotube is it enough to compute the difference between the total energy by varying the distance between them.

[zh]

Yes, the way mentioned by you will work if the size of your supercell for a two capped nanotube is large enough.

[Zexter]

can you please tell me the procedure to vary the distance between the nanotubes iteratively and to compute the energy according to the calculator defined for each iteration. I have a (5,5)nanotube with 5 repetitions making a structure with capped ends to 137 atoms. So would it be enough for your supercell stuff? the two capped nanotubes make around 2*137 atoms.Whether I want to reduce the atom count or proceed with the same structure

[Zexter]

whether the potential energy of the capped nanotube system plotted with respect to distance of separation between the two nanotube would give the potential energy minima of the system

[zh]

whether the potential energy of the capped nanotube system plotted with respect to distance of separation between the two nanotube would give the potential energy minima of the system

Yes, it does.

[Zexter]

ok. the minima in the potential energy curve with distance give the potential energy minima. But I can have only the total energy of the system(the capped nanotubes) with me . So whether the total energy in this case is equal to the potential energy or else I want select some other option in the analysis part  


how the total energy is equal to the potential energy in this case

[zh]

Usually, the potential energy curve means the total energy of a system with respect to a distance, e.g. the distance between two nanotubes in your case. In other word, the term of "potential energy" is improperly used in your question.

To obtain the interaction energy between two capped CNTs, one may follow the procedure used to calculate the total energy of O2 as a function of  the distance between two O atoms:
i) assume that the distance between two capped CNTs is d;
ii) calculate the total energies (E_tot) of two capped CNTs with different values of d;
iii) calculate the total energies of each capped CNTs, separately. assume that they are E_tot(1) and E_tot(2), respectively;
iii) from the minimum energy (E_min) in the curve of E_tot vs d, the interaction energy will be E_min - E_tot(1) - E_tot(2).

[Zexter]

Whether the same procedure adapted to calculate the interaction between the concentric walls of the double walled nanotube is followed even to calculate the in plane interaction between two capped cnt each one is single walled .
What's the reason to calculate the energy of the capped cnt's separately .
I have attached the image of such a kind here .

[zh]

For the atomic configuration shown in your attached image, it is one CNT with two caps due to the periodicity along the c direction. To simulate the interaction between two CNTs each with one cap, a second vacuum layer is needed to be introduced in the c direction. In this case, for each CNT one of its end is capped and the other one is open.  To simulate the interaction between two CNTs each with two caps at the ends, a second vacuum layer is also needed.  

[Zexter]

could you please tell me the why a vaccum layer has to be introduced and the procedure to introduce the same in my code.

What's the role played by vaccum layer and its effect  here

If I am not dfining the vaccum layer what errors would result

the c direction you are specifying is the z direction here. So if I plot the distance vs total energy of a system as above, Is the curve is wrong  even if I followed your procedure described in the previous posts to get the values.

[zh]

The vacuum layer can be introduced by making the lattice constant c larger than the the length of CNT.
In the last reply, it is clearly said that the model built in your attached image corresponds to one CNT with two caps at the ends. That model cannot be used to simulate the interaction between two CNTs.

 

[Zexter]

Sorry I am not getting the lattice constant c. How can be it be greater than CNT length which would be on a much larger scale.
So if my model is wrong then give a procedure to get the interaction between the structure of a similar kind
My theme is to get the interaction between two cnts of same type armchair (n,n) on their capped end side.

[zh]

A schematic configuration for the simulation of interaction between two CNTs is shown in my attached image.

Using this model, the interaction energy between two CNTs each with one cap at the end can be obtained by calculating the total energy of such configuration as a function of d (i.e., the distance between two caps of CNTs) or c (i.e., the lattice constant along the c direction since c = d1+L1+d+L2+d2, as shown in the image.). Here the vacuum thickness d1+d2 should be large enough.

[Zexter]

fine. whether d1 and d2 must be large enough than d or d1 and d2 greater than l1 and l2. what is the constraint you meant